Winter cover cropping to improve soil health in semiarid, irrigated cropping systems of Central Oregon

A 1-year experiment was conducted in Madras, OR, to examine the ability of winter cover crops (CCs) to improve physical, chemical, and biological soil properties over a bare fallow control. Competition for water is frequently seen as an obstacle to cover cropping in semiarid, irrigated systems. Benefits from CCs need to be demonstrated and quantified in regions such as Central Oregon's high desert for growers to make cost/benefit analysis decisions. To support such decisions, the effect of eight winter CC treatments (two brassicas, four legumes, two cereal mixtures) on five agronomic parameters and 39 soil health indicators (0–5 cm) were measured in the spring of 2019 after 8 months of CC growth. We identified four soil indicator response patterns in reference to the fallow: (i) steady improvement over fallow across all CCs (16 indicators, with hairy vetch and turnip being most efficient); (ii) marked improvement over fallow but somewhat constant response among CCs (organic C and N, surface hardness); (iii) negligible change from fallow; and (iv) varied response to CCs including both a deterioration and an improvement of soil health. Overall, 13 soil health indicators and five agronomic parameters responded significantly to CC treatment. CCs generated a stronger response of soil chemical and biological parameters than physical (average 82%, 79%, and 18% improvement over fallow, respectively). Hairy vetch had the greatest positive impact on soil biological and chemical properties but the lowest average impact on physical indicators. Winter CCs do offer soil health benefits in Central Oregon but should not be viewed as a short-term fix to physical soil deficiencies. Our study provides strong evidence for the general ability of CCs to improve soil health in water-limited systems. It also demonstrates the need for further studies focused on multiyear rotations, especially related to the improvement of soil physical properties such as soil moisture availability.